This invention relates generally to support elements, and, more particularly, to a support link which is primarily used for structural support in an environment in which thermal isolation is an essential consideration.
The need for very low temperature cooling is becoming more evident as both missile surveillance and space satellite tracking programs move toward new operational systems. Passive radiators have been used in the past to cool infrared detectors to temperatures on the order of 100.degree. K. These radiators were designed for relatively small heat loads, on the order of a few milliwatts. They were flown on satellites in sun-synchronous or geosynchronous orbits. Viewing requirements for the sensor combined with proximity requirements between the radiator and sensor dictated the need for radiators with conical specularly reflecting shields to minimize incident environmental energy. Contamination of these specular surfaces by condensable materials degraded their performance and required periodic warmup of the surfaces to drive off contaminants.
Development of cryogenic heat pipes made it possible to locate a cyrogenic radiator away from the earth-viewing sensor. In a sun-synchronous or geosynchronous orbit, this means that the radiator can be shielded from any direct solar or earth incident heat flux; hence specularly reflecting surfaces are no longer required. This significantly reduces or eliminates the problem of contamination of cyrogenic radiator coatings.
The remaining obstacle to providing passive cooling for infrared space surveillance systems was temperature. Space surveillance and satellite tracking systems generally require long wavelength infrared (LWIR) systems, which must be operated below 20.degree. K. Even with high-performance multilayer insulation systems, passive radiators were limited to temperatures near or above 100.degree. K. because of parasitic heat leakage from the warm spacecraft to the cold radiator surface. In recent years, however, significant technology advancements in two areas have considerably brightened the outlook for passively cooled IR surveillance systems. The first was in the area of detector technology with the development of hybrid charge coupled device (CCD) detectors, which can be operated in the medium to long wavelength region (8-14 microns) at temperatures in the range of 40.degree. to 70.degree. K. The second advancement was development of the multistage heat-pipe radiator concept. Use of staged radiators in conjunction with cyrogenic heat pipes makes it possible to reject significant heat loads at temperatures as low as 40.degree. K. or below.
The multistage heat pipe radiator concept utilizes two or more radiator stages. Each stage is thermally isolated from the other by multilayer insulation and by support links in order to minimize heat conduction. The principle of performance is based on each radiator stage intercepting the parasitic heat leakage through the insulation below and radiating it to space such that each successive stage sees a colder and colder boundary temperature. This process allows each successive stage to attain lower and lower temperatures. The intermediate stages can also provide heat rejection at intermediate temperature levels to cool other elements of a system such as optics, baffles, and electronics. Heat pipes transport heat from the heat source to the radiator and distribute it over the radiator surface to increase overall fin efficiency.
It is therefore essential in the future development of multistage heat pipe radiators to be able to minimize heat transfer between stages. A need therefore arises to devise structural support elements or links which are capable of not only providing sufficient structural support for such multistage heat pipe radiators but also providing the required thermal isolation between stages.